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Adding fractions

 To add (or subtract) two fractions, they must have the same denominator: When the denominators are different, we cannot just add the numerators.
Before we can add those two fractions, we must find equivalent fractions with the same denominators. This is how we do it:
  1. We calculate the lowest common multiple of the denominators:

      The l.c.m. of 2 and 5 is 10: we can divide 10 into 2 and into 5:

  2. We use the l.c.m. as the common denominator:

  3. We divide the common denominator by the original denominator of each fraction, and multiply the result by its numerator:

  4. We use the result as the new numerators.Then we calculate the result as before:
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